The present invention relates generally to the field of broadcast antenna designs. More particularly, the present invention relates to the design of a television broadcast antenna that would allow for simultaneous UHF and either low- or mid-band VHF broadcast with equal or less wind load than existing VHF only antennas.
Under the rules of the Federal Communication Commission (FCC), by the year 2006 television broadcasters are required to transition from current National Television System Committee (NTSC) antenna systems to digital television (DTV) antenna systems. NTSC antenna systems are analog systems and during operation of analog NTSC systems only one television transmission signal is transmitted per channel. Typically NTSC television antennas transmit either one very high frequency (VHF) channel or one ultra high frequency (UHF) channel.
DTV is a new type of broadcasting technology. So far the FCC has allocated mostly UHF Channels for DTV broadcasts. DTV antenna systems transmit the information used to make television pictures and sounds by data bits, rather than by waveforms, as performed by NTSC systems. With DTV, broadcasters will be able to provide television programming of a higher resolution and better picture quality than what can be provided under the current analog
NTSC antenna systems. In addition, DTV broadcasters will be able to transmit more than one signal per channel, and thus, deliver more than one television program per station.
The majority of antennas used for UHF transmission in NTSC systems are slotted coaxial designs. UHF slotted coaxial antennas gained widespread use in NTSC broadcasting because of their above-average performance characteristics, namely excellent omni-directional azimuth patterns, low wind loads, and smooth null fill.
While the foregoing performance characteristics are also desirable for DTV transmission, the more stringent antenna output performance standards of DTV transmission cannot be met with current slotted coaxial antenna designs. At the present stage of antenna development, the antenna output response performance across multiple channels, which was given little consideration in NTSC systems, is now an important parameter for DTV transmission.
For example, when used as television broadcasting antennas, slotted coaxial antennas are generally optimized to transmit signals for a specified television channel having a six MHz bandwidth. For NTSC transmission, the power distribution across the six MHz bandwidth is concentrated at three basic carrier frequencies, namely, picture, color and aural. Therefore, the performance of the antenna is critical only at these three carrier frequencies.
However, for DTV transmission, the power is equally distributed across a 5.4 MHz frequency span within the six MHz bandwidth. Therefore, the antenna""s performance is critical across substantially the entire operating band. This means that the antenna""s elevation pattern must remain stable (i.e. unchanged) at all frequencies within the bandwidth, and not just at isolated frequencies.
Use of existing UHF slotted coaxial antennas for DTV transmission is therefore hindered by the fact that slotted coaxial antennas are not suitable for multi-channel applications, such as simultaneous UHF and VHF signaling. This is due in part to the fact that the slots are not broadband radiators.
All current analog TV broadcasts, including all current VHF broadcasts, will be phased out by the end of 2006. During the transition to DTV, broadcasters will be operating both analog (NTSC) and digital (DTV) channels.
This presents a problem, especially to VHF broadcasters that have been assigned UHF/DTV channels, because VHF television broadcasters are faced with having to transmit television programming on two antenna systems, the conventional analog VHF/NTSC antenna system and the DTV antenna system. This is a problem for broadcasters because many towers are not strong enough to accept the additional windload of a second antenna.
Accordingly, it is desirable to provide a UHF slotted coaxial antenna that transmits DTV signals with excellent omni-directional azimuth patterns, low wind loads, and smooth null fill. It is also desirable to provide a replacement antenna that would allow for simultaneous UHF and either low or mid-band VHF broadcast with equal or less wind load than existing VHF only antennas, and thus reduce the wind load on the antenna tower structure.
In one aspect of the present invention an antenna is provided that includes a coaxial antenna having an inner conductor and an outer conductor, a batwing assembly mounted to the outer conductor of the coaxial antenna, and a feed line for feeding the batwing assembly separately from the coaxial antenna.
In another aspect of the present invention the batwing assembly includes four planar wings.
In another aspect of the present invention, the planar wings are spaced concentrically around the outer conductor.
In another respect of the present invention, the coaxial antenna transmits a UHF signal and the batwing assembly transmits a VHF signal.
In another aspect of the present invention, the inner conductor includes a transmission line inner conductor and a transmission line outer conductor.
In another aspect of the present invention, the transmission line inner conductor is made from copper.
In another aspect of the present invention, the outer conductor is made from steel.
In another aspect of the present invention, the inner conductor is connected to a center feed.
In another aspect of the present invention, the center feed is substantially intermediate a top spoke short and a bottom spoke short.
In another aspect of the present invention, an antenna is provided that includes a means for transmitting a UHF signal, a means mounted to the UHF antenna means for transmitting VHF signal, and a feed means for feeding the UHF signal transmitting means separate from the VHF signal transmitting means.
In another aspect of the present invention, a method of constructing a UHF and VHF broadcast antenna is provided that includes forming a coaxial antenna having an inner conductor and an outer conductor, mounting a batwing assembly to the outer conductor of the coaxial antenna, and connecting a feed line to the batwing assembly.
There has thus been outlined, rather broadly, the more important features of the invention in order that the detailed description thereof that follows may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional features of the invention that will be described below and which will form the subject matter of the claims appended hereto.
In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein, as well as the abstract, are for the purpose of description and should not be regarded as limiting.
As such, those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention.